Apparatus for raising and lowering heavy loads

ABSTRACT

Apparatus for raising and lowering heavy loads, such as ships, locomotives, heavy staging or the like loads, comprising a plurality of cross members arranged in adjacent spaced relationship and provided at both ends respectively with a displacing device raisable and lowerable in a vertical guide member and formed by two parts relatively displaceable in the lifting and lowering direction by means of a pressure medium, each device having at least one locking member engaging in recesses of the associated guide member and displaceable by the pressure medium transversely to the lifting direction, and at the same time the two locking members of each displacing device arranged in vertical spaced relationship engage alternately as an abutment in a recess for raising and lowering with displacement of one part relative to the other and, for holding the load, both locking members engage in respective recesses.

[ 51 Oct. 15,1974

United States atent 1 1 Klinkhammer et al.

1,403,920 5/1965 France...........................r......2l2/64 l l APPARATUS FOR RAISING AND LOWERING HEAVY LOADS Primary ExaminerRichard A. Schacher Assistant Examiner-Jeffrey V. Nase n e g n m out f a .ww r may n mE mm. im kB Md e K KS s r o t n e V m H both of Germany Attorney, Agent, or FirmSteinberg & Blake ABSTRACT [22] Filed:

Apparatus for raising and lowering heavy loads, such as ships, locomotives, heavy staging or the like loads comprising a plurality of cross members arranged in adjacent spaced relationship and provided at both [30] Foreign Application Priority Data Mar. 6, 1972 Austria 1863/72 finds respectively with a displacing device raisable and lowerable in a vertical guide member and formed by -hn gtte- .l a w wmmcmwm l a flmm d m a em mmw fie v wm mfl m mhm m m m m a w m awod d e .1 P10 Or. o a mf erm swn i in h uemmtm wd &meve 6 h n a r mnt n -rg n er GD. 3 en I recee ba m m nwm wfmumfie b m m a wdmm S .1 mnnw wm antm S307. an a .1 amS n d t C m m C ea n V. w m mw .I SUI .l. b S .Bhatn W m SM SfaHm n 8m fd m h hmo o erdn ctf l rcfife ah r e Oh e Sa t n r p .i..n .S C O e OdeC p bt S fle miw mmflfimwmflm f fi tdradbS.mOmC 44 4 wm um xx l 3 57 29 65 1 2 l/ oo 2 M 63 0 61 1 6 B i ,5 0011 u 5 "u 6HWS9B S mm U H JA T mm 6 m m m I R W9 an m m n e .1M .nP mm M 25 S mm 1 m m. fiE wm H mm cT m m m m m m A m "44 rT.w U SHP m m 2 .m w Ww mw m WSN ww L 7 N// C m U v.9 d S. M 69 U IF 6 l 1] l 2 8 6 MM 5 BB 5 H 1 FOREIGN PATENTS OR APPLICATIONS 64,223 12/1955 212/57 9 Claims, 11 Drawing Figures PATENTEBBBT 1 51914 3.8413141 v SHEEI 10F 3 L IL lllFlll! llll more particularly, ships, are known, in which a plurality of adjacent cross members forming a lifting platform are designed to be raised and lowered by means of cable winches or rack drives provided on both sides of the platform.

The disadvantages of these conventional lifting devices reside in the expensive construction, since two comparatively expensive cable winches or rack drives are necessary for each cross member in addition, the lifting means are exposed to soiling and corrosion, due to their location mainly in water, and this restricts the method of operating the lifting means and shortens their useful life.

Furthermore, the lifting height is limited and the freedom of lateral movement of the loads restricted at the highest point of the lift.

It is an object of the present invention, whilst minimizing the previous deficiencies, to provide an improved apparatus for lifting and lowering heavy loads, said apparatus being simple and economical to construct, having a reliable operation free of breakdowns with loads of any weight and being designed to have a long life,

Furthermore, this apparatus is intended to make any desired lifting heights possible and to allow freedom of movement of the raised load in any direction for further transport. I

According to the present invention, there is provided an apparatus for raising and lowering heavy loads, such as ships, locomotives, heavy staging or the like loads,

comprising a plurality of cross members arranged in adjacent spaced relationship and provided at both ends respectively with a displacing device raisable and lowerable in a vertical guide member and formed by two parts relatively displaceable in the lifting and lowering direction by means ofa pressure medium, each device having at least one locking member engaging in recesses of the associated guide member and displaceable by the pressure medium transversely to the lifting direction, and at the same time the two locking members of each displacing device arranged in vertical spaced relationship engage alternately as an abutment in a recess for raising and lowering with displacement of one part relative to the other and, for holding the load, both locking members engage in respective recesses.

It is preferable to provide the two displaceable parts of the displacing device, forming a telescopic unit, with two locking members respectively, opposed to each other, displaceable by the pressure medium in opposite directions. extending transversely to the lifting and lowering direction and engaging in respective recesses in the guide member.

One displaceable part may be formed by a cylindrical housing and the other displaceable part by a piston having a piston rod and the locking members may each be designed as a pin with a piston provided at its end remote from the locking end.

At the end of its piston rod remote from the piston, the pistonlike displaceable part is provided with a cylindrical chamber formed by a part of the housing in placeable part shaped like a cylindrical housing and having a cylindrical chamber for the piston of the other displaceable part, is provided near its end opposed to the end having a passage for the piston rod of the other displaceable part with a second cylindrical chamber in which both locking members, displaceable in opposite directions by their pistons are mounted.

The two displaceable parts and the locking members are preferably displaceable dependently on each other and in succession by a common pressure medium, such as oil, air or the like, whilst, for lifting and lowering, a pair of locking members is always displaceable in an unlocking position after which one part is displaced whilst the other pair of locking members remain, as an abutment, in engagement with the guide member."

The guide members may be formed by a U-rail having in both sides of the U-shaped member opposing recesses arranged in vertical spaced relationship, the

spacing of two adjacent superimposed recesses corresponding to the spacing of the superimposed locking members when the displaceable parts are pushed together, this condition simultaneously determining the lifting height of a working stroke. I

A plurality of guide members, such as rollers, slide rails or the like, may be provided, at least on one, preferably on both ends of the displacing device, on the top of one displaceable part and on the underside of the other displaceable part, which guide members dispose themselves in the corner regions of the cross-bar of the guide rail and in corner areas of the guide rail formed by contact rails secured to the free ends of the sides of the U.

Each cross member can be connected to the displacing device at both its ends by respective bearing bolts engaging in a bearing member of the upper displaceable part the bearing bolt of one end of the cross member being displaceably held in a bore in the bearing member and the bearing bolt of the other end of the cross member being displaceably held in a slotof a bearing member for the possibility of longitudinal expansion of the cross member.

The lifting apparatus of the present invention is simple and economical to design and has a long life, as well as providing a reliable lifting and lowering function.

A particular advantage is the compact and externally sealed construction of the displacing devices which are provided at both ends of each cross member and are displaceable upwardly and downwardly in stages or variable in vertical guide rails the displacing devices preferably operate with a pressure medium, which requires only a few pressure medium ducts for each displacing device. The entire displacing mechanism is protected against soiling or corrosion and requires very little maintenance. In these displacing devices the load is carried by mechanical parts when the cross members are in a resting condition and there is no undesirable supporting of the load by the pressure medium.

The individual displacing devices are preferably positively controlled, i.e., their mechanical locking members are actuated by the pressure medium and determine by their position engagement with the vertical guides or released from their vertical guides the possibility of lifting'and lowering; in the raising and lowering process some locking members are always in mechanical engagement with the guides and thus form a reliable abutment.

The lifting heights may be formed as high as desired by the advantageously designed and operating displacing devices without any changes being made to said displacing devices, only the vertical guides co-operating therewith have to be adjusted in their length to the particular lifting heights.

The lifting speed of the driving devices is infinitely adjustable by the pressure medium and the synchronous control of all the displacing devices can be effected by simple monitoring of the working strokes.

By means of the present invention, loads of any weight can be raised and lowered and the present invention is particularly suitable for the raising of ships in docks.

Since the vertical guides and the displacing device are located or moved within the range of the lifting height, no devices projecting upwardly or laterally are present at the maximum lifting position so that the raised load can be conveyed further without movement in a horizontal or inclined plane in all directions.

Another important advantage of the present invention may be seen inthe feature that, due to the compact, closed, construction of each displacing device, said displacing device can be arranged in the water (sea water) without influencing its construction (damage by corrosion) and its function, and there is also no risk of the displaceable parts becoming iced-up icing up would not restrict operation because of its closed construction.

Furthermore, the displacing devices of the present invention require no electrical switches which are difficult to provide under water and are susceptible to damage.

Since all the moveable parts (displaceable parts and locking members) are controlled by a pressure medium dependently on each other, incorrect movements ofthe above-mentioned parts are impossible and the reliable operation (raising and lowering movements) of the present invention is ensured.

The invention will be further illustrated by way of example, with reference to the accompanying drawings, in which:

FIG. I is a schematic view of an apparatus for lifting and lowering heavy loads, for example, a ship comprising a plurality of cross members raisable on vertical guides, and acting as a lifting platform;

FIG. 2 is a front elevational view of two guide members provided in adjacent spaced relationship and a cross member vertically displaceable in the guide members by means of a displacing device provided at both ends;

FIG. 3 is a side view of a guide member mounted on a securing rail and having a displacing device located therein;

FIG. 4 is a cross-sectional view through a guide member formed by a U-shaped rail and having a displacing device guided therein, taken on the line I-I of FIG. 3;

FIG. 5 is a longitudinal section through a displacing device located in a guide member; and

FIGS. 6 to 11 show schematic views ofa guide member with a displacing device located therein in the course of movement during a lifting stroke.

A plurality of cross members 10, e.g., girders arranged in adjacent spaced relationship and forming a lifting platform are associated with an apparatus according to the present invention for raising and lowering heavy loads, more particularly water craft (ships 11), track vehicles (locomotives), heavy staging members or the like loads.

Each cross member 10 is provided at both ends with a displacing device 12, by which each cross member 10 is raisably and lowerably held in vertical guide members 13 in stages or is variably adjustable for lifting and lowering.

The individual cross members 10 are preferably disposed in adjacent parallel spaced relationship and, in accordance with these cross members 10, a guide member 13 is provided for each end of these cross members.

The guide members 13 may be secured to a mounting surface 28, such as a dock wall, pile planking or the like of a dock 27 or other mounting surfaces 28 for the lifting apparatus and each surface 28 extends longitudinally in a vertical plane. All the displacing devices 12 are identically constructed and have the same mode of operation. The displacing device 12 comprises two parts 14 and 15 displaceable relative to each other by means of a pressure medium in a raising and lowering direction, as lifting and lowering members, to each of which at least one locking member 17, displaceable transversely to the lifting and lowering direction by the pressure medium and engaging in recesses 16 of the associated guide member 13, is provided; the two locking members 17 of the displacing device 12 arranged in vertical spaced relationship may be locked alternately in a recess 16 as an abutment for lifting and lowering with displacement of one part 14 or 15 relative to the other part 15 or 14 and, for holding the load (with the displacing device 12 stationary), both locking members 17 are inserted in respective recesses 16, so that the displacing device 12 is always partially or entirely mechanically secured in position, during the lifting and lowering movement, as well as in the holding position. The two displaceable parts 14 and 15, forming a telescopic unit, are preferably provided with two opposed locking members 17 displaceable by the pressure medium in opposing directions, extending transversely to the lifting direction and each engaging in a recess 16 in the guide member 13.

One displaceable part 14 is formed by a cylindrical housing and the other displaceable part 15 by a piston 15a having a piston rod 15b. The locking members 17 are preferably formed by a pin provided with a piston 17a fitted on the end remote from the locking end (the end adjacent to the guide member 13, and having a circular, angular or oval cross-section.)

At the end of its piston rod 15b remote from the piston 15a, the piston-like displaceable part 15 has a cylindrical chamber 18 which is formed by a housing member 15c and in which the two locking members 17, opposed to each other at the same level, are displaceably mounted'with their pistons 17a.

The displaceable body 14, constructed as a cylindrical housing, comprises a cylindrical chamber 19 for the piston 15a of the displaceable part and one end, remote from the end in which a passage is provided for the piston rod 15b of the displaceable part, has a second cylindrical chamber 20 in which the two locking members 17, opposed to each other and also provided at the.

same level, aredisplaceably mounted with their pistons device 12 are preferably arranged so as to be displaceable at right angles to the lifting and lowering directions. two locking members 17 being displaceable by the pressure medium in opposite directions as a pair located at a common level.

The movement of the two displaceable parts 14 and relatively to each other and the displacement of the locking members 17 effected outwardly or inwardly is achieved by a common pressure medium, such as oil, air, or the like, the movement of the displaceable parts 14, 15 and 17 being effected dependently of each other and in succession.

The cylindrical housing represents the upper displaceable part 14 and the piston-shaped displaceable part 15 is arranged at the bottom, the cylindrical housing 14 being provided at its upper end, and the piston rod 1512 at its lower end, with the cylindrical chambers and 18 for the locking members 17.

The cylindrical housing 14 has an oblong shape with an angular cross-section such as a square or rectangular cross-section and the housing member 15c of the displaceable part 15 is adapted in cross-section to that of the displaceable part 14.

The guide members 13 are formed for example by U shaped rails having recesses 16 formed in their two sides 13a extending at least approximately parallel to each other, the spacing of the adjacent, superimposed recesses 16 corresponding to the spacing of the superimposed locking members 17 when the parts 14 and 15 are pushed together.

In the two sides 13a of the U-shaped member, the recesses are formed oppositely to each other at the same level and the space between two superimposed recesses 16 corresponds to a lifting or lowering movement in one working stroke of the displacing device 12.

In order to make it possible for the locking pins 17 to engage with very little friction in the recesses 16 in the rail, said recesses are lined with slide bushes 16a and the locking pins 17 are chamfered and/or rounded at their free ends; the locking pins 17 engage and fit in the recesses 16 (16a).

The width of the displaceable part 14 and the housing member l5c approximately corresponds to the spacing of the sides of the U-shaped guide rails, so that this forms a certain guide means for the raising and lowering movement of the displaceable parts 14 and 15.

However, it is preferable to secure guide members 21, such as rollers, slide bars or the like to one end, preferably to both'ends, of the displacing devices 12 to the top of the cylindrical housing 14 and to the underside of the housing member 150 which members are preferably arranged with their plane of movement or sliding planes on the diagonal lines of the angular cross-sectional form of the displacing device 12 two guide members 13 locate themselves in the corners of the U-shaped rail and the other two guide members 21 in respective corners formed by contact strips (13b) secured to the free ends of the sides 13a of the U-shaped members (FIG. 4) and guide the displacing device 12 without tilting during the raising and lowering movement.

The cross member 10 is held at both ends by a bearing bolt 22 in bearing members 23, such as fork members, of the upper side of the displacing device 12; the bearing members 23 are secured to the cylindrical housing 14 and support the cross member 10 by their bearing bolts 22. It is preferable to arrange the bearing bolts 22 at one end of the cross member in a bore of the bearing member 23 and, at the other end in a slot 23a of the bearing member 23, thus making longitudinal expansion of the traverse possible during fluctuations of 5 temperature.

Each guide member 13 is suspended at its upper end from a mounting rail 25 by a bearing bolt 24.

Supply and discharge ducts 26 of each displacing device 12 extend into the cylindrical housing 14 or the displaceable part 15 at the top, at the bottom or at an upper level.

The raising and lowering ofthe displacing devices 12 is effected as follows, only the operation being described here with reference to one displacingdevice, since all the displacing devices operate in the same manner.

FIG. 5 shows the locked position of the displacing device 12 in the loaded or unloaded condition all the locking members 17 engage in the recesses 16 of the two sides 13a of the guide rail and the displacing device 12 is mechanically secured in position.

If a lifting motion is to be executed, the two upper.

locking members 17 of the displaceable body 14 are first moved by the pressure medium out of the recesses 16 and into the part 20 so that the displaceable part 14 is released for moving upwardly (FIG. 6). Thepressure medium is then able to flow into the cylindrical chamber 19 and acts on the piston 15a, the displaceable part 14 being gradually displaced'upwardly bythe inflowing pressure medium until the cylindrical chamber 19 has been displaced throughout its entire length by means of the piston 15a. During this lifting movement of the part 14, the locking members 17 of the'lower displaceable part 15 located in the recesses '16 form an abutment (FIG. 7). When the entire lifting movement of the displaceable part 15 is concluded, the upper locking members 17 are pushed outwardly again into the recesses 16 of the guide rail 13 by the pressure medium and the displacing device 12 is secured by all the fourlocking members 17 (FIG. 8), the two displaceable parts 14 and 15 being separated. The lower locking members 17 are then drawn out by the pressure medium and the displaceable part 15 is released for moving upwardly (FIG. 9).

The pressure medium then acts on the piston rod end surface of the piston 15a and displaces said piston 15a in the cylindrical chamber 19 upwardly to the end of said cylindrical chamber 19 the entire displaceable part 15 moves upwardly (FIG. 10). When this displacement of the part 15 is concluded, the pressure medium presses the lower locking members 17 outwardly again into the recesses 16 and the displacing device 12 is secured mechanically in position again by'all the locking members 17 (FIG. 11). A working stroke is now terminated and the displacing device-l2 raised by one stroke; these working strokes are repeated several times until the desired height isreached. The lowering of the displacing device 12 is effected accordingly in the reverse sequence, whilst likewise during the displacement of one part 14 or 15, the other part 15 or. 14

is mechanically secured in position by its locking mem-' bers.

In the arrangement of a displacing device 12 in each end region of the cross member 10, a step-by-step raising and lowering of the cross member is possible; if each cross member 10 is provided at both ends with two displacing devices 12, they can be raised and lowered variably, the displacing devices 12 overlapping each other in the course of movement during one lifting stroke. The displacement of all the displaceable parts 14, and 17 of the displacing device 12 is preferably effected by a specially controlled pressure medium controlled for the movement of a following part dependently on the movement of the preceding part; however, separate connecting ducts and a specific control of the pressure medium may be provided for each displaceable part, all of these means being subject however to a central control in their mode of operation.

Thus it will be seen that with the structure of the invention the apparatus for raising and lowering heavy loads includes the elongated upright guide wall means 13 which is formed with the openings 16 situated at different elevations along this guide wall means 13. The unit 12 forms a fluid-pressure raising-and-lowering means which is guided for up-and-down movement by the guide wall means 13, this fluid-pressure raising-and lowering means 12 having the upper end region where the chamber is formed and the lower end region where the chamber 18 is formed. The fluid-pressure raising-and-lowering means 12 includes the cylinderand-piston means 14, 15 for carrying out contracting and expanding movements which respectively decrease and increase the distance between the opposed upper and lower end regions of the fluid-pressure raising-andlowering means 12. The portions of the upper and lower end regions of the means 12 which are formed with the chambers 20 and 18, which respectively have horizontal axes, form parts of a pair of fluid-pressure holding means which includes the retractable upper and lower piston means 17 which have the outer free ends capable of entering into and being retracted from the openings 16 of the guide wall means 13. This pair of fluid-pressure holding means and the fluid-pressure raising-and-lowering means coact with each other in such a way that the fluid-pressure holding means alternately displaces the upper and lower piston means 17 into and out of the openings 16 in timed relation with the expanding and contracting movements of the means 12 during movement of the latter along the guide wall means 13. The upper end region of the means 12 is operatively connected with the component 10 which forms a support means for carrying a load, this support means 10 being movable together with the fluid-pressure raising-and-lowering means 12.

We claim:

1. In an apparatus for raising and lowering heavy loads, elongated upright guide wall means formed with openings situated at different elevations along said guide wall means, fluid-pressure raising-and-lowering means guided for up-and-down movement by said guide wall means and having opposed upper and lower end regions, said fluid-pressure means including a cylinder and piston means for carrying out contracting and expanding movements respectively decreasing and increasing the distance between said end regions, a pair offluid-pressure holding means respectively situated at said end regions and including parts of said end regions which are formed with hollow chambers respectively having horizontal axes and a pair of retractable piston means respectively movable in said chambers and having outer holding ends movable beyond said end regions into and out of said openings of said guide wall means, said pair of fluid-pressure holding means and said fluid-pressure raising-and-lowering means cooperating with each other for alternately displacing said piston means of said pair of fluid-pressure holding means into and out of openings of said guide wall means in timed relation with said contracting and expanding movements of said fluid-pressure raising-and-lowering means during stepwise movement of the latter along said guide wall means, and support means for carrying a load, said support means being operatively connected with the upper end region of said fluid-pressure raisingand-lowering means for movement with said upper end region.

2. The combination of claim 1 and wherein the retractable piston means of said pair of fluid-pressure holding means respectively move along said horizontal axes perpendicularly to a common axis of the cylinder and piston means of said fluid-pressure raising-andlowering means.

3. The combination of claim 1 and wherein said guide wall means is in the form of an elongated channel of substantially U-shaped cross section having opposed walls respectively formed with said openings, and said retractable piston means of said fluid-pressure holding means each including a pair of opposed pistons for moving simultaneously into and out of a pair of openings of said opposed walls of said guide wall means.

4. The combination of claim 1 and wherein said openings of said guide wall means carry sleeves which line said openings, respectively, and said holding ends of said retractable piston means have ends which facilitate their entry into said sleeves.

5. The combination of claim 1 and wherein said guide wall means is in the form of an elongated-channel of substantially U-shaped cross section having a pair of opposed walls between which said fluid-pressure raising-and-lowering means is located, and the latter means having a width which is only slightly less than the distance between said opposed walls to be guided by the latter.

6. The combination of claim 1 and wherein a pair of said elongated upright guide wall means extend parallel to each other and a pair of said fluid-pressure raisingand-lowering means are respectively guided by said pair ofguide wall means with each raising-and-lowering means having said pair of fluid-pressure holding means, and a single elongated support means extending between and operatively connected to said upper end regions of the pair of fluid-pressure raising-and-lowering means, so that a pair of the latter means act on a support means to raise and lower the same.

7. The combination of claim 1 and wherein a means is operatively connected with an upper end of said elongated guide wall means for carrying said guide wall means in a manner according to which the latter is suspended at said upper end thereof.

8. The combination of claim 1 and wherein said cylinder and piston means of said fluid-pressure raisingand-lowering means includes a cylinder housing and a piston movable therein and having a piston rod extending beyond said housing and terminating outside of said housing in an enlarged portion which is formed with one of said chambers which receives one of said pair of retractable piston means of said fluid-pressure holding means.

9. The combination of claim 8 and wherein said cylinder housing has distant from the chamber carried by said piston of said fluid-pressure raising-and-lowering means beyond said cylinder housing a wall portion forming one of said end regions and formed with a chamber which receives the other of said retractable piston means. 

1. In an apparatus for raising and lowering heavy loads, elongated upright guide wall means formed with openings situated at different elevations along said guide wall means, fluidpressure raising-and-lowering means guided for up-and-down movement by said guide wall means and having opposed upper and lower end regions, said fluid-pressure means including a cylinder and piston means for carrying out contracting and expanding movements respectively decreasing and increasing the distance between said end regions, a pair of fluid-pressure holding means respectively situated at said end regions and including parts of said end regions which are formed with hollow chambers respectively having horizontal axes and a pair of retractable piston means respectively movable in said chambers and having outer holding ends movable beyond said end regions into and out of said openings of said guide wall means, said pair of fluidpressure holding means and said fluid-pressure raising-andlowering means cooperating with each other for alternately displacing said piston means of said pair of fluid-pressure holding means into and out of openings of said guide wall means in timed relation with said contracting and expanding movements of said fluid-pressure raising-and-lowering means during stepwise movement of the latter along said guide wall means, and support means for carrying a load, said support means being operatively connected with the upper end region of said fluid-pressure raising-and-lowering means for movement with said upper end region.
 2. The combination of claim 1 and wherein the retractable piston means of said pair of fluid-pressure holding means respectively move along said horizontal axes perpendicularly to a common axis of the cylinder and piston means of said fluid-pressure raising-and-lowering means.
 3. The combination of claim 1 and wherein said guide wall means is in the form of an elongated channel of substantially U-shaped cross section having opposed walls respectively formed with said openings, and said retractable piston means of said fluid-pressure holding means each including a pair of opposed pistons for moving simultaneously into and out of a pair of openings of said opposed walls of said guide wall means.
 4. The combination of claim 1 and wherein said openings of said guide wall means carry sleeves which line said openings, respectively, and said holding ends of said retractable piston means have ends which facilitate their entry into said sleeves.
 5. The combination of claim 1 and wherein said guide wall means is in the form of an elongated channel of substantially U-shaped cross section having a pair of opposed walls between which said fluid-pressure raising-and-lowering means is located, and the latter means having a width which is only slightly less than the distance between said opposed walls to be guided by the latter.
 6. The combination of claim 1 and wherein a pair of said elongated upright guide wall means extend parallel to each other and a pair of said fluid-pressure raising-and-lowering means are respectively guided by said pair of guide wall means with each raising-and-lowering means having said pair of fluid-pressure holding means, and a single elongated support means extending between and operatively connected to said upper end regions of the pair of fluid-pressure raising-and-lowering means, so that a pair of the latter means act on a support means to raise and lower the same.
 7. The combination of claim 1 and wherein a means is operatively connected with an upper end of said elongated guide wall means for carrying said guide wall means in a manner according to which the latter is suspended at said upper end thereof.
 8. The combination of claim 1 and wherein said cylinder and piston means of said fluid-pressure raising-and-lowering means includes a cylinder housing and a piston movable therein and having a piston rod extending beyond said housing and terminating outside of said housing in an enlarged portion which is formed with one of said chambers which receives one of said pair of retractable piston means of said fluid-pressure holding means.
 9. The combination of claim 8 and wherein said cylinder housing has distant from the chamber carried by said piston of said fluid-pressure raising-and-lowering means beyond said cylinder housing a wall portion forming one of said end regions and formed with a chamber which receives the other of said retractable piston means. 